1. Field of the Invention
The invention relates to a mask, and in particular to a mask with hydrophobic surface.
2. Description of the Related Art
One cause of mask malfunction is contaminants formed thereon, that is, precipitate. The main components of the precipitate are ammonium sulfate or hydrocarbon organic compounds. Mask compositions, mask clean condition, mask storage condition, or environmental exposure are related to precipitate formation. Currently, methods have been provided to solve the precipitate issue, for example, reducing total concentration of sulfur and ammonia within the environment or using low-outgassing material to prepare and store masks. However, as the wavelength of the exposure source is reduced from 254 nm to 193 nm, photo-induced chemical reaction occurs more easily in the airtight space between the pellicle and mask, resulting in more serious precipitate formation.
FIG. 1 shows precipitate formation on a conventional mask surface. The mask 1 comprises a substrate 2, a plurality of patterns 3 formed on the substrate 2, and a pellicle 4 mounted on the substrate 2 through a pellicle frame 5. Precipitate 6 is formed on the substrate 2 due to highly reactive environment and high surface energy on substrate.
To prolong mask lifetime, development of methods to avoid precipitate formation on the mask surface is required. Reducing the surface energy of the mask to create a hydrophobic and chemically inert surface is a feasible aspect thereof.